QConcatenateTablesProxyModel crushes being sourceModel in QSortFilterProxyModel

TLDR:

Following assertion has to be removed from QConcatenateTablesProxyModel::index method:

// qconcatenatetablesproxymodel.cpp:292
Q_ASSERT(hasIndex(row, column, parent));

Digging into problem

Sample code:

QSortFilterProxyModel proxy;
QConcatenateTablesProxyModel concat;
proxy.setSourceModel(&concat);

This example crushes when we try to remove the last sourceModel from concat. When there're no columns left in the concat, proxy updates it's information and calls this slot:

// qsortfilterproxymodel.cpp:1785
void QSortFilterProxyModelPrivate::_q_sourceColumnsRemoved(
// ...
    proxy_sort_column = q->mapFromSource(model->index(0,source_sort_column, source_parent)).column();
}

where source_sort_column = -1 (even if we set it to some reasonble value).
But model doesn't have index(0,-1), so it crashes at the mentioned assertion.

At the same moment, this example is fully functional running in release mode, because the assertion (being removed in the release mode) follows this simple condition:

// qconcatenatetablesproxymodel.cpp:292
Q_ASSERT(hasIndex(row, column, parent));
if (!hasIndex(row, column, parent))
    return QModelIndex();

Is it correct to remove Q_ASSERT?

Compare QAbstractItemModel::index implementations:

QModelIndex QConcatenateTablesProxyModel::index(int row, int column, const QModelIndex &parent) const
{
    Q_D(const QConcatenateTablesProxyModel);
    Q_ASSERT(hasIndex(row, column, parent));
    if (!hasIndex(row, column, parent))
        return QModelIndex();
    Q_ASSERT(checkIndex(parent, QAbstractItemModel::CheckIndexOption::ParentIsInvalid)); // flat model
    const auto result = d->sourceModelForRow(row);
    Q_ASSERT(result.sourceModel);
    return mapFromSource(result.sourceModel->index(result.sourceRow, column));
}

QModelIndex QAbstractListModel::index(int row, int column, const QModelIndex &parent) const
{
    return hasIndex(row, column, parent) ? createIndex(row, column) : QModelIndex();
}

QAbstractListModel doesn't have any assertions on hasIndex, so should not QConcatenateTablesProxyModel.